Polymer blends with improved rheology and improved unnotched impact strength

ABSTRACT

This invention relates to a blend of biodegradable polymers comprising:
     (A) about 15% to about 60% by weight of at least one flexible biodegradable polymer (A) having a glass transition less than about 0° C.,   (B) about 85% to about 40% by weight of at least one rigid biodegradable polymer (B) having a glass transition greater than about 10° C.;
 
said percentages being based on the total weight of the polymer blend;
 
wherein said polymer blend has a unnotched Izod impact strength according to ASTM D256 of at least 9 ft-lbs/in at 23° C. In one embodiment, the polymer blend has a unnotched Izod impact strength according to ASTM D256 at least 20 ft-lbs/in at 23° C.

RELATED APPLICATIONS

This application claims priority to and the benefit of the followingapplications; U.S. Patent Ser. No. 60/531,599, filed Dec. 22, 2003,incorporated herein by reference; U.S. Patent Ser. No. 60/531,723, filedDec. 22, 2003, incorporated herein by reference; and U.S. patent Ser.No. 11/005,587 filed on even date herewith entitled “Polymer Blends WithImproved Notched Impact Strength”, incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to biodegradable polymer blends.Preferably, the present invention relates to blends of two biopolymers,such as biodegradable polyesters and polyester amides, in order to yieldblends with improved rheology and unnotched Izod impact strength. Thebiodegradable polymer blends may be suitable for a number ofapplications.

BACKGROUND OF THE INVENTION

Biodegradable materials are comprised of components which, by microbialcatalyzed degradation, are reduced in strength by reduction in polymersize to monomers or short chains which are then assimilated by themicrobes. In an aerobic environment, these monomers or short chains areultimately oxidized to CO₂, H₂O, and new cell biomass. In an anaerobicenvironment the monomers or short chains are ultimately oxidized to CO₂,H₂O, acetate, methane, and cell biomass. Successful biodegradationrequires that direct physical contact must be established between thebiodegradable material and the active microbial population or theenzymes produced by the active microbial population. An active microbialpopulation useful for degrading the films and blends of the inventioncan generally be obtained from any municipal or industrial wastewatertreatment facility in which the influents (waste stream) are high incellulose materials. Moreover, successful biodegradation requires thatcertain minimal physical and chemical requirements be met such assuitable pH, temperature, oxygen concentration, proper nutrients, andmoisture level.

In response to the demand for biopolymers, a number of new biopolymershave been developed which have been shown to biodegrade when discardedinto the environment.

Currently known biopolymers have unique properties, benefits andweaknesses. For example, some of the biopolymers tend to be strong butalso quite rigid and brittle. This makes them poor candidates whenflexible sheets or films are desired, such as for use in making wraps,bags and other packaging materials requiring good bend and foldingcapability. For other bipolymers, it is not believed that films can beblown from them.

On the other hand, biopolymers such as PCL, and certain aliphaticaromatic polyesters currently available in the market are many timesmore flexible compared to the more rigid biopolymers discussedimmediately above. However, they have relatively low melting points suchthat they tend to be self adhering when newly processed and/or exposedto heat. While easily blown into films, such films are difficult toprocess on a mass scale since they will tend to self adhere when rolledonto spools, which is typically required for sale and transport to otherlocations and companies. To prevent self-adhesion (or “blocking”) ofsuch films, it is typically necessary to incorporate silica or otherfillers. As the aforementioned example for blowing films suggests, themolding, extruding, and forming of thicker parts is also extremelydifficult.

Another important criterion for extrusion profiles, extrusion blowmolded articles and/or film and sheet is temperature stability.“Temperature stability” is the ability to maintain desired propertieseven when exposed to elevated or depressed temperatures, or a largerange of temperatures, which may be encountered during shipping orstorage. For example, many of the more flexible biopolymers tend tobecome soft and sticky if heated significantly above room temperature,thus compromising their ability to maintain their desired packagingproperties. Other polymers can become rigid and brittle upon beingcooled significantly below freezing (i.e., 0° C.). Thus, a singlehomopolymer or copolymer may not by itself have sufficient stabilitywithin large temperature ranges.

In view of the foregoing, it would be an advancement in the art toprovide biodegradable polymer blends with improved unnotched Izod impactstrength which can be readily formed into extrusion profiles or readilyextrusion blow molded, or blown film or extruded into film and sheetsthat have increased temperature stability over a broad range oftemperatures compared to existing biopolymers.

BRIEF SUMMARY OF THE INVENTION

The present invention discloses specific biodegradable polymer blendcomposition ranges having improved rheology and unnotched Izod impactstrength. Such polymer blends may be readily formed into extrusionprofiles, extrusion blow molded, or formed into films and sheets for usein a wide variety of applications requiring rigidity, toughness, andbiodegradability.

In a first embodiment, the polymer blend of the invention comprises:

-   (A) about 15% to about 60% by weight of at least one flexible    biodegradable polymer (A) having a glass transition temperature of    less than about 0° C.; and-   (B) about 85% to about 40% by weight of at least one rigid    biodegradable polymer (B) having a glass transition temperature    greater than about 10° C.;    said percentages being based on the total weight of the polymer    blend;    wherein said polymer blend has an unnotched Izod impact strength    according to ASTM D256 of at least 9 ft-lbs/in at 0° C. and at    23° C. In one embodiment, the polymer blend has an unnotched Izod    impact strength according to ASTM D256 of at least 20 ft-lbs/in at    23° C.

In a second embodiment of the invention, a polymer blend is provided,comprising:

-   (A) about 15% to about 60% by weight of at least one polymer (A)    having a glass transition temperature of less than about 0° C.,    wherein said polymer (A) comprises:    -   (1) diacid residues comprising about 1 to 65 mole percent        aromatic dicarboxylic acid residues; and 99 to about 35 mole        percent of non-aromatic dicarboxylic acid residues selected from        the group consisting of aliphatic dicarboxylic acids residues        containing from about 4 to 14 carbon atoms and cycloaliphatic        dicarboxylic acids residues containing from about 5 to 15 carbon        atoms; wherein the total mole percent of diacid residues is        equal to 100 mole percent; and    -   (2) diol residues selected from the group consisting of one or        more aliphatic diols containing about 2 to 8 carbon atoms,        polyalkylene ethers containing about 2 to 8 carbon atoms, and        cycloaliphatic diols containing from about 4 to 12 carbon atoms;        wherein the total mole percent of diol residues is equal to 100        mole percent; and-   (B) about 85% to about 40% by weight of at least one polymer (B),    wherein said polymer (B) is a biopolymer derived from polylactic    acid;    said percentages being based on from the total weight of the polymer    blend;    wherein said polymer blend has an unnotched Izod impact strength    according to ASTM D256 of at least 9 ft-lbs/in at 0° C. and at    23° C. In one embodiment, the polymer blend has an unnotched Izod    impact strength according to ASTM D256 of at least 20 ft-lbs/in at    23° C.

In a third embodiment of the invention is a polymer blend comprising:

-   (A) about 15% to about 50% by weight of at least one polymer (A))    having a glass transition temperature of less than about 0° C.,    wherein said polymer (A) consists essentially of:    -   (1) aromatic dicarboxylic acid residues comprising about 35 to        65 mole percent of terephthalic acid residues and 65 to about 35        mole percent of adipic acid residues, glutaric acid residues, or        combinations of adipic acid residues and glutaric acid residues;        and    -   (2) diol residues consisting of 1,4-butanediol; and-   (B) about 85% to about 50% by weight of at least one polymer (B),    wherein said polymer (B) is a biopolymer derived from polylactic    acid;    said percentages being based on the total weight of the polymer    blend wherein said polymer blend has an unnotched Izod impact    strength according to ASTM D256 of at least 9 ft-lbs/in at 0° C. and    at 23° C. In one embodiment, the polymer blend has an unnotched Izod    impact strength according to ASTM D256 of at least 20 ft-lbs/in at    23° C.

In a fourth embodiment of the invention is a polymer blend comprising:

-   (A) about 25% to about 50% by weight of at least one polymer (A)),    having a glass transition temperature of less than about 0° C.,    wherein said polymer (A) consists essentially of:    -   (1) aromatic dicarboxylic acid residues comprising about 35 to        65 mole percent of terephthalic acid residues and 65 to about 35        mole percent of adipic acid residues, glutaric acid residues, or        combinations of adipic acid residues and glutaric acid residues;        and    -   (2) diol residues consisting of 1,4-butanediol; and-   (B) about 75% to about 50% by weight of at least one polymer (B),    wherein said polymer (B) is a biopolymer derived from polylactic    acid;    said percentages being based on the total weight of the polymer    blend wherein said polymer blend has an unnotched Izod impact    strength according to ASTM D256 of at least 9 ft-lbs/in at 0° C. and    at 23° C. In one embodiment, the polymer blend has an unnotched Izod    impact strength according to ASTM D256 of at least 20 ft-lbs/in at    23° C.

In a fifth embodiment of the invention is a polymer blend comprising:

-   (A) about 40% to about 60% by weight of at least one polymer (A))    having a glass transition temperature of less than about 0C, wherein    said polymer (A) consists essentially of:    -   (1) aromatic dicarboxylic acid residues comprising about 35 to        65 mole percent of terephthalic acid residues and 65 to about 35        mole percent of adipic acid residues, glutaric acid residues, or        combinations of adipic acid residues and glutaric acid residues;        and    -   (2) diol residues consisting of 1,4-butanediol; and-   (B) about 60% to about 40% by weight of at least one polymer (B)    wherein said polymer (B) is a biopolymer derived from polylactic    acid;    said percentages being based on the total weight of the polymer    blend wherein said polymer blend has an unnotched Izod impact    strength according to ASTM D256 of at least 9 ft-lbs/in at 0° C. and    at 23° C. In one embodiment, the polymer blend has an unnotched Izod    impact strength according to ASTM D256 of at least 20 ft-lbs/in at    23° C.

In a sixth embodiment of the invention is a polymer blend comprising:

-   (A) about 40% to about 50% by weight of at least one polymer (A))    having a glass transition temperature of less than about 0° C.,    wherein said polymer (A) consists essentially of:    -   (1) aromatic dicarboxylic acid residues comprising about 35 to        65 mole percent of terephthalic acid residues and 65 to about 35        mole percent of adipic acid residues, glutaric acid residues, or        combinations of adipic acid residues and glutaric acid residues;        and    -   (2) diol residues consisting of 1,4-butanediol; and.-   (B) about 50% to about 40% by weight of at least one polymer (B)    wherein said polymer (B) is a biopolymer derived from polylactic    acid;    said percentages being based on the total weight of the polymer    blend wherein said polymer blend has an unnotched Izod impact    strength according to ASTM D256 of at least 9 ft-lbs/in at 0° C. and    at 23° C. In one embodiment, the polymer blend has an unnotched Izod    impact strength according to ASTM D256 of at least 20 ft-lbs/in at    23° C.

For all of the described embodiments, the polymer blends may compriseabout 1 to about 50 weight % of biodegradable additives, based on thetotal weight of the polymer blend.

These biodegradable polymer blends provide improved unnotched Izodimpact strength which can be readily formed into extrusion profiles orreadily extrusion blow molded into formed articles that have increasedtemperature stability over a broad range of temperatures compared toexisting biopolymer blends.

DETAILED DESCRIPTION

The invention achieves the foregoing improvements by blending at leastone biopolymer having relatively high stiffiess (rigid), hereinafteralso referred to as “biopolymer(s) (B)”, with at least one biopolymer(A) having relatively high flexibility, hereinafter also referred to as“biopolymer(s) (A)”. The novel blends have improved rheology andunnotched Izod impact strength when compared to the individual polymercomponents. Moreover, such blends are superior to conventional plastics,which suffer from their inability to degrade when discarded in theenvironment.

Unless otherwise indicated, all numbers expressing quantities ofingredients, properties such as molecular weight, reaction conditions,and so forth used in the specification and claims are to be understoodas being modified in all instances by the term “about.” Accordingly,unless indicated to the contrary, the numerical parameters set forth inthe following specification and attached claims are approximations thatmay vary depending upon the desired properties sought to be obtained bythe present invention. At the very least, each numerical parametershould at least be construed in light of the number of reportedsignificant digits and by applying ordinary rounding techniques.Further, the ranges stated in this disclosure and the claims areintended to include the entire range specifically and not just theendpoint(s). For example, a range stated to be 0 to 10 is intended todisclose all whole numbers between 0 and 10 such as, for example 1, 2,3, 4, etc., all fractional numbers between 0 and 10, for example 1.5,2.3, 4.57, 6.1113, etc., and the endpoints 0 and 10. Also, a rangeassociated with chemical substituent groups such as, for example, “C1 toC5 hydrocarbons”, is intended to specifically include and disclose C1and C5 hydrocarbons as well as C2, C3, and C4 hydrocarbons.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements.

Any of the weight percentages described herein for one embodiment may beused in combination with other embodiments.

As described herein, the polymer blend of the invention generallycomprises the following embodiment as well as others described herein:

-   (A) about 15% to about 60% by weight of at least one flexible    biodegradable polymer (A) having a glass transition temperature of    less than about 0° C.; and-   (B) about 85% to about 40% by weight of at least one rigid    biodegradable polymer (B) having a glass transition temperature    greater than about 10° C.;    the percentages being based on the total weight of the polymer    blend;    wherein the polymer blend has an unnotched Izod impact strength    according to ASTM D256 of at least 9 ft-lbs/in at 0° C. and at    23° C. In one embodiment, the polymer blend has an unnotched Izod    impact strength according to ASTM D256 of at least 20 ft-lbs/in at    23° C.

In response to the demand for biopolymers, a number of new biopolymershave been developed which have been shown to biodegrade when discardedinto the environment. Some of these are aliphatic-aromatic copolyesters,polyesteramides, a modified polyethylene terephthalate, polymers basedon polylactic acid, polymers known as polyhydroxyalkanoates (PHA), whichinclude polyhydroxybutyrates (PHB), polyhydroxyvalerates (PHV), andpolyhydroxybutyrate-hydroxyvalerate copolymers (PHBV), andpolycaprolactone (PCL).

The polymer blends according to the invention include at least onebiopolymer having relatively high stiffness and at least one biopolymerhaving relatively high flexibility. When blended together in the correctproportions, it is possible to derive the beneficial properties fromeach polymer while offsetting or eliminating the negative properties ofeach polymer if used separately to molded, extruded, or formed parts fora broad variety of applications. By blending a relatively rigid polymerwith a relatively flexible polymer in certain proportions, the inventorshave discovered that the improved rheology and unnotched Izod impactstrength of the blend exceed the desirable properties of each polymerwhen used individually. Thus, the surprising result of an unexpectedsynergistic effect has been demonstrated.

Biopolymers (A) that may be characterized as being generally “flexible”include those polymers having a glass transition temperature of lessthan about 0° C. In one embodiments, the flexible biopolymers (A) willhave a glass transition temperature of less than about −10° C. In otherembodiments of the invention, the flexible biopolymers will have a glasstransition temperature of less than about −20° C., and even morepreferably, less than about −30° C.

Examples of soft or flexible biopolymers (A) include but are not limitedto the following: aliphatic-aromatic copolyesters (such as thosemanufactured by BASF and previously manufactured by Eastman ChemicalCompany), aliphatic polyesters which comprise repeating units having atleast 5 carbon atoms, e.g., polyhydroxyvalerate,polyhydroxybutyrate-hydroxyvalerate copolymer and polycaprolactone (suchas those manufactured by Daicel Chemical, Monsanto, Solvay, and UnionCarbide), and succinate-based aliphatic polymers, e.g., polybutylenesuccinate (PBS), polybutylene succinate adipate (PBSA), and polyethylenesuccinate (PES) (such as those manufactured by Showa High Polymer).

The term “polyester”, as used herein, is intended to include“copolyesters” and is understood to mean a synthetic polymer prepared bythe polycondensation of one or more difunctional carboxylic acids withone or more difunctional hydroxyl compounds. Typically the difinctionalcarboxylic acid is a dicarboxylic acid and the difunctional hydroxylcompound is a dihydric alcohol such as, for example, glycols and diols.The term “residue”, as used herein, means any organic structureincorporated into a polymer or plasticizer through a polycondensationreaction involving the corresponding monomer. The term “repeating unit”,as used herein, means an organic structure having a dicarboxylic acidresidue and a diol residue bonded through a carbonyloxy group. Thus, thedicarboxylic acid residues may be derived from a dicarboxylic acidmonomer or its associated acid halides, esters, salts, anhydrides, ormixtures thereof. As used herein, therefore, the term dicarboxylic acidis intended to include dicarboxylic acids and any derivative of adicarboxylic acid, including its associated acid halides, esters,half-esters, salts, half-salts, anhydrides, mixed anhydrides, ormixtures thereof, useful in a polycondensation process with a diol tomake a high molecular weight polyester.

The polyester(s) included in the present invention contain substantiallyequal molar proportions of acid residues (100 mole %) and diol residues(100 mole %) which react in substantially equal proportions such thatthe total moles of repeating units is equal to 100 mole %. The molepercentages provided in the present disclosure, therefore, may be basedon the total moles of acid residues, the total moles of diol residues,or the total moles of repeating units. For example, a copolyestercontaining 30 mole % adipic acid, based on the total acid residues,means that the copolyester contains 30 mole % adipic residues out of atotal of 100 mole % acid residues. Thus, there are 30 moles of adipicresidues among every 100 moles of acid residues. In another example, acopolyester containing 30 mole % 1,6-hexanediol, based on the total diolresidues, means that the copolyester contains 30 mole % 1,6-hexanediolresidues out of a total of 100 mole % diol residues. Thus, there are 30moles of 1,6-hexanediol residues among every 100 moles of diol residues.

In one embodiment of this invention, the polymer blends of the inventioncomprise aliphatic-aromatic copolyesters referred to as AAPE herein)constituting component (A) of the present invention include thosedescribed in U.S. Pat. Nos. 5,661,193, 5,599,858, 5,580,911 and5,446,079, the disclosures of which are incorporated herein byreference.

In one embodiment, a “flexible” polymer that may be used in themanufacture of the inventive polymer blends includes aliphatic-aromaticcopolyesters manufactured by BASF and sold under the trade name ECOFLEX.The aliphatic-aromatic copolyesters manufactured by BASF comprise astatistical copolyester derived from 1,4-butanediol, adipic acid, anddimethylterephthalate (DMT). In some cases, a diisocyanate is used as achain lengthener.

The copolyester composition of this invention may comprise one or moreAAPE's which may be a linear, random copolyester or branched and/orchain extended copolyester comprising diol residues which contain theresidues of one or more substituted or unsubstituted, linear orbranched, diols selected from aliphatic diols containing 2 to about 8carbon atoms, polyalkylene ether glycols containing 2 to 8 carbon atoms,and cycloaliphatic diols containing about 4 to about 12 carbon atoms.The substituted diols, typically, will contain 1 to about 4 substituentsindependently selected from halo, C6-C10 aryl, and C1-C4 alkoxy.Examples of diols which may be used include, but are not limited to,ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol,2,2-dimethyl-1,3-propanediol, 1,3-butanediol, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, polyethylene glycol, diethylene glycol,2,2,4-trimethyl-1,6-hexanediol, thiodiethanol,1,3-cyclohexanedimethanol, 1,4-cyclo-hexanedimethanol,2,2,4,4-tetramethyl-1,3-cyclobutanediol, triethylene glycol, andtetraethylene glycol. Aliphatic diols are preferred in one embodiment.In another embodiment, more preferred diols comprising one or more diolsselected from 1,4-butanediol; 1,3-propanediol; ethylene glycol;1,6-hexanediol; diethylene glycol; and 1,4-cyclohexanedimethanol. In yetanother embodiment, 1, 4-butanediol, ethylene glycol and1,4-cyclohexanedimethanol,singly, or in combination, are preferred, butnot required.

The AAPE also comprises diacid residues which contain about 35 to about99 mole %, preferably about 35 to about 75 mole %, more preferably,about 35 to about 65 mole %, and even more preferably, about 40 to about60 mole %, based on the total moles of acid residues, of the residues ofone or more substituted or unsubstituted, linear or branched,non-aromatic dicarboxylic acids selected from aliphatic dicarboxylicacids containing 2 to about 12 carbon atoms and cycloaliphaticdicarboxylic acids containing about 5 to about 10 carbon atoms. Thesubstituted non-aromatic dicarboxylic acids will typically contain 1 toabout 4 substituents selected from halo, C6-C10 aryl, and C1-C4 alkoxy.Non-limiting examples of aliphatic and cycloaliphatic dicarboxylic acidsinclude malonic, succinic, glutaric, adipic, pimelic, azelaic, sebacic,fumaric, 2,2-dimethyl glutaric, suberic, 1,3-cyclopentanedicarboxylic,1,4-cyclohexanedicarboxylic, 1,3-cyclohexanedicarboxylic, diglycolic,itaconic, maleic, and 2,5-norbomanedicarboxylic. In addition to thenon-aromatic dicarboxylic acids, the AAPE comprises about 1 to about 65mole percent %, preferably about 25 to 65 mole percent, more preferably,about 35 to 65 mole percent, and even more preferably, about 60 to 40mole percent, based on the total moles of acid residues, of the residuesof one or more substituted or unsubstituted aromatic dicarboxylic acidscontaining 6 to about 10 carbon atoms. In the case where substitutedaromatic dicarboxylic acids are used, they will typically contain 1 toabout 4 substituents selected from halo, C6-C10 aryl, and C1-C4 alkoxy.Non-limiting examples of aromatic dicarboxylic acids which may be usedin the AAPE of our invention are terephthalic acid, isophthalic acid,salts of 5-sulfoisophthalic acid, and 2,6-naphthalenedicarboxylic acid.In another embodiment, the AAPE comprises diol residues comprising theresidues of one or more of: 1,4-butanediol; 1,3-propanediol; ethyleneglycol; 1,6-hexanediol; diethylene glycol; or 1,4-cyclohexanedimethanol;and diacid residues comprising (i) about 35 to about 99 mole percent,preferably about 35 to about 75 mole percent, more preferably about 40to 60 mole percent, based on the total moles of acid residues, of theresidues of one or more non-aromatic dicarboxylic acids selected fromglutaric acid, diglycolic acid, succinic acid,1,4-cyclohexanedicarboxylic acid, and adipic acid (preferably, glutaricacid and adipic acid, either singly or in combination); (ii) about 5 toabout 65 mole percent, preferably about 25 to 65 mole percent, morepreferably, about 35 to 65 mole percent, and even more preferably, about40 to 60 mole percent,based on the total moles of acid residues, of theresidues of one or more aromatic dicarboxylic acids selected fromterephthalic acid and isophthalic acid. More preferably, thenon-aromatic dicarboxylic acid may comprise adipic acid and the aromaticdicarboxylic acid may comprise terephthalic acid. In one embodiment, thediol will comprise about 95 to about 100 mole %, preferably 100 mole %,of 1,4-butanediol.

In one embodiment, it is preferred that the AAPE comprise terephthalicacid in the amount of about 25 to about 65 mole %, preferably about 35to about 65 mole %, and even more preferably, about 40 to about 60 mole%. Also, it is preferred that the AAPE comprise adipic acid in theamount of about 75 to about 35 mole %, preferably about 65 to about 35mole %, and even more preferably, about 60 to about 40 mole %.

Other preferred compositions for the AAPE's of the present invention arethose prepared from the following diols and dicarboxylic acids (orcopolyester-forming equivalents thereof such as diesters) in thefollowing mole percent, based on 100 mole percent of a diacid componentand 100 mole percent of a diol component:

-   (1) glutaric acid (about 30 to about 75%); terephthalic acid (about    25 to about 70%); 1,4-butanediol (about 90 to 100%); and modifying    diol (0 about 10%);-   (2) succinic acid (about 30 to about 95%); terephthalic acid (about    5 to about 70%); 1,4-butanediol (about 90 to 100%); and modifying    diol (0 to about 10%); and-   (3) adipic acid (about 30 to about 75%); terephthalic acid (about 25    to about 70%); 1,4-butanediol (about 90 to 100%); and modifying diol    (0 to about 10%).

In one embodiment, one or more modifying diols are selected from1,4-cyclohexanedimethanol, triethylene glycol, polyethylene glycol andneopentyl glycol. Some AAPE's may be linear, branched or chain extendedcopolyesters comprising about 50 to about 60 mole percent adipic acidresidues, about 40 to about 50 mole percent terephthalic acid residues,and at least 95 mole percent 1,4-butanediol residues. Even morepreferably, the adipic acid residues are present in the amount of fromabout 55 to about 60 mole percent, the terephthalic acid residues arepresent in the amount of from about 40 to about 45 mole percent, and the1,4-butanediol residues are present in the amount of from about 95 to100 mole percent. Such compositions have recently been commerciallyavailable under the trademark Eastar Bio® copolyester from EastmanChemical Company, Kingsport, Tenn.

Additionally, specific examples of preferred AAPE's include apoly(tetra-methylene glutarate-co-terephthalate) containing (a) 50 molepercent glutaric acid residues, 50 mole percent terephthalic acidresidues and 100 mole percent 1,4-butanediol residues, (b) 60 molepercent glutaric acid residues, 40 mole percent terephthalic acidresidues and 100 mole percent 1,4-butanediol residues or (c) 40 molepercent glutaric acid residues, 60 mole percent terephthalic acidresidues and 100 mole percent 1,4-butanediol residues; apoly(tetramethylene succinate-co-terephthalate) containing (a) 85 molepercent succinic acid residues, 15 mole percent terephthalic acidresidues and 100 mole percent 1,4-butanediol residues or (b) 70 molepercent succinic acid residues, 30 mole percent terephthalic acidresidues and 100 mole percent 1,4-butanediol residues; a poly(ethylenesuccinate-co-terephthalate) containing 70 mole percent succinic acidresidues, 30 mole percent terephthalic acid residues and 100 molepercent ethylene glycol residues; and a poly(tetramethyleneadipate-co-terephthalate) containing (a) 85 mole percent adipic acidresidues, 15 mole percent terephthalic acid residues and 100 molepercent 1,4-butanediol residues or (b) 55 mole percent adipic acidresidues, 45 mole percent terephthalic acid residues and 100 molepercent 1,4-butanediol residues.

The AAPE preferably comprises from about 10 to about 1,000 repeatingunits and preferably, from about 15 to about 600 repeating units. TheAAPE preferably also has an inherent viscosity of about 0.4 to about 2.0dL/g, more preferably about 0.7 to about 1.4, as measured at atemperature of 25° C. using a concentration of 0.5 gram copolyester in100 ml of a 60/40 by weight solution of phenol/tetrachloroethane.

In addition, “flexible” (A) polymers will preferably have aconcentration in a range from about 15% to about 60% by weight of thebiodegradable polymer blend, and in other embodiments, the rigidpolymers (B) will preferably have a concentration in ranges of about 15to about 50% by weight, about 25% to about 50% by weight, and 40% toabout 59% by weight, based on the total weight of the polymer blend.

Any of the biopolymers, including but not limited to the AAPE,optionally, may contain the residues of a branching agent. In oneembodiment, the weight percentage ranges for the branching agent arefrom about 0 to about 2 weight (weight % in this invention refers toweight %), preferably about 0.1 to about 1 weight %, and most preferablyabout 0.1 to about 0.5 weight % based on the total weight of the AAPE.The branching agent preferably has a weight average molecular weight ofabout 50 to about 5000, more preferably about 92 to about 3000, and afunctionality of about 3 to about 6. For example, the branching agentmay be the esterified residue of a polyol having 3 to 6 hydroxyl groups,a polycarboxylic acid having 3 or 4 carboxyl groups (or ester-formingequivalent groups ) or a hydroxy acid having a total of 3 to 6 hydroxyland carboxyl groups.

Representative low molecular weight polyols that may be employed asbranching agents include glycerol, trimethylolpropane,trimethylolethane, polyethertriols, glycerol, 1,2,4-butanetriol,pentaerythritol, 1,2,6-hexanetriol, sorbitol, 1,1,4,4,-tetrakis(hydroxymethyl) cyclohexane, tris(2-hydroxyethyl) isocyanurate, anddipentaerythritol. Particular branching agent examples of highermolecular weight polyols (MW 400-3000) are triols derived by condensingalkylene oxides having 2 to 3 carbons, such as ethylene oxide andporpylene oxide with polyol initiators. Representative polycarboxylicacids that may be used as branching agents include hemimellitic acid,trimellitic (1,2,4-benzenetricarboxylic) acid and anhydride, trimesic(1,3,5-benzenetricarboxylic) acid, pyromellitic acid and anhydride,benzenetetracarboxylic acid, benzophenone tetracarboxylic acid,1,1,2,2-ethane-tetracarboxylic acid, 1,1,2-ethanetricarboxylic acid,1,3,5-pentanetricarboxylic acid, and 1,2,3,4-cyclopentanetetracarboxylicacid. Although the acids may be used as such, preferably they are usedin the form of their lower alkyl esters or their cyclic anhydrides inthose instances where cyclic anhydrides can be formed. Representativehydroxy acids as branching agents include malic acid, citric acid,tartaric acid, 3-hydroxyglutaric acid, mucic acid, trihydroxyglutaricacid, 4-carboxyphthalic anhydride, hydroxyisophthalic acid, and4-(beta-hydroxyethyl)phthalic acid. Such hydroxy acids contain acombination of 3 or more hydroxyl and carboxyl groups. Especiallypreferred branching agents include trimellitic acid, trimesic acid,pentaerythritol, trimethylol propane and 1,2,4-butanetriol.

The aliphatic-aromatic polyesters of the invention also may comprise oneor more ion-containing monomers to increase their melt viscosity. It ispreferred that the ion-containing monomer is selected from salts ofsulfoisophthalic acid or a derivative thereof. A typical example of thistype of monomer is sodiosulfoisophthalic acid or the dimethyl ester ofsodiosulfoisophthalic. The preferred concentration range forion-containing monomers is about 0.3 to about 5.0 mole %, and, morepreferably, about 0.3 to about 2.0 mole %, based on the total moles ofacid residues.

One example of a branched AAPE of the present invention ispoly-(tetramethylene adipate-co-terephthalate) containing 100 molepercent 1,4-butanediol residues, 43 mole percent terephthalic acidresidues and 57 mole percent adipic acid residues and branched withabout 0.5 weight percent pentaerythritol. This AAPE may be produced bythe transesterification and polycondensation of dimethyl adipate,dimethyl terephthalate, pentaerythritol and 1,4-butanediol. The AAPE maybe prepared by any conventional method known in the art such as heatingthe monomers at 190° C. for 1 hour, 200° C. for 2 hours, 210° C. for 1hour, then at 250° C. for 1.5 hours under vacuum in the presence of 100ppm of Ti present initially as titanium tetraisopropoxide.

Another example of a branched AAPE is poly(tetramethyleneadipate-co-terephthalate) containing 100 mole percent 1,4-butanediolresidues, 43 mole percent terephthalic acid residues and 57 mole percentadipic acid residues and branched with 0.3 weight percent pyromelliticdianhydride. This AAPE is produced via reactive extrusion of linear poly(tetramethylene adipate-co-terephthalate) with pyromellitic dianhydrideusing an extruder.

The AAPE of the instant invention also may comprise from 0 to about 5weight %, and in one embodiment, from 0.1 to 5 weight %, based on thetotal weight of the composition, of one or more chain extenders.Exemplary chain extenders are divinyl ethers such as those disclosed inU.S. Pat. No. 5,817,721 or diisocyanates such as, for example, thosedisclosed in U.S. Pat. No. 6,303,677. Representative divinyl ethers are1,4-butanediol divinyl ether, 1,5-hexanediol divinyl ether and1,4-cyclohexandimethanol divinyl ether.

Representative diisocyanates are toluene 2,4-diisocyanate, toluene2,6-diisocyanate, 2,4′-diphenylmethane diisocyanate,naphthylene-1,5-diisocyanate, xylylene diisocyanate, hexamethylenediisocyanate, isophorone diisocyanate andmethylenebis(2-isocyanatocyclohexane). The preferred diisocyanate ishexamethylene diisocyanate. The weight percent ranges are preferablyabout 0.3 to about 3.5 wt %, based on the total weight percent of theAAPE, and most preferably about 0.5 to about 2.5 wt %. It is alsopossible in principle to employ trifunctional isocyanate compounds whichmay contain isocyanurate and/or biurea groups with a functionality ofnot less than three, or to replace the diisocyanate compounds partiallyby tri-or polyisocyanates.

The AAPE's of the instant invention are readily prepared from theappropriate dicarboxylic acids, esters, anhydrides, or salts, theappropriate diol or diol mixtures, and any branching agents usingtypical polycondensation reaction conditions. They may be made bycontinuous, semi-continuous, and batch modes of operation and mayutilize a variety of reactor types. Examples of suitable reactor typesinclude, but are not limited to, stirred tank, continuous stirred tank,slurry, tubular, wiped-film, falling film, or extrusion reactors. Theterm “continuous” as used herein means a process wherein reactants areintroduced and products withdrawn simultaneously in an uninterruptedmanner. By “continuous” it is meant that the process is substantially orcompletely continuous in operation in contrast to a “batch” process.“Continuous” is not meant in any way to prohibit normal interruptions inthe continuity of the process due to, for example, start-up, reactormaintenance, or scheduled shut down periods. The term “batch” process asused herein means a process wherein all the reactants are added to thereactor and then processed according to a predetermined course ofreaction during which no material is fed or removed into the reactor.The term “semicontinuous” means a process where some of the reactantsare charged at the beginning of the process and the remaining reactantsare fed continuously as the reaction progresses. Alternatively, asemicontinuous process may also include a process similar to a batchprocess in which all the reactants are added at the beginning of theprocess except that one or more of the products are removed continuouslyas the reaction progresses. The process is operated advantageously as acontinuous process for economic reasons and to produce superiorcoloration of the polymer as the copolyester may deteriorate inappearance if allowed to reside in a reactor at an elevated temperaturefor too long a duration.

The AAPE's of the present invention are prepared by procedures known topersons skilled in the art and described, for example, in U.S. Pat. No.2,012,267. Such reactions are usually carried out at temperatures from150° C. to 300° C. in the presence of polycondensation catalysts suchas, for example, alkoxy titanium compounds, alkali metal hydroxides andalcoholates, salts of organic carboxylic acids, alkyl tin compounds,metal oxides, and the like. The catalysts are typically employed inamounts between 10 to 1000 ppm, based on total weight of the reactants.

The reaction of the diol and dicarboxylic acid may be carried out usingconventional copolyester polymerization conditions. For example, whenpreparing the copolyester by means of an ester interchange reaction,i.e., from the ester form of the dicarboxylic acid components, thereaction process may comprise two steps. In the first step, the diolcomponent and the dicarboxylic acid component, such as, for example,dimethyl terephthalate, are reacted at elevated temperatures, typically,about 150° C. to about 250° C. for about 0.5 to about 8 hours atpressures ranging from about 0.0 kPa gauge to about 414 kPa gauge (60pounds per square inch, “psig”). Preferably, the temperature for theester interchange reaction ranges from about 180° C. to about 230° C.for about 1 to about 4 hours while the preferred pressure ranges fromabout 103 kPa gauge (15 psig) to about 276 kPa gauge (40 psig).Thereafter, the reaction product is heated under higher temperatures andunder reduced pressure to form the AAPE with the elimination of diol,which is readily volatilized under these conditions and removed from thesystem. This second step, or poly-condensation step, is continued underhigher vacuum and a temperature which generally ranges from about 230°C. to about 350° C., preferably about 250° C. to about 310° C. and, mostpreferably, about 260° C. to about 290° C. for about 0.1 to about 6hours, or preferably, for about 0.2 to about 2 hours, until a polymerhaving the desired degree of polymerization, as determined by inherentviscosity, is obtained. The polycondensation step may be conducted underreduced pressure which ranges from about 53 kPa (400 torr) to about0.013 kPa (0.1 torr). Stirring or appropriate conditions are used inboth stages to ensure adequate heat transfer and surface renewal of thereaction mixture. The reaction rates of both stages are increased byappropriate catalysts such as, for example, titanium tetrachloride,manganese diacetate, antimony oxide, dibutyl tin diacetate, zincchloride, or combinations thereof. A three-stage manufacturingprocedure, similar to that described in U.S. Pat. No. 5,290,631, mayalso be used, particularly when a mixed monomer feed of acids and estersis employed. For example, a typical aliphatic-aromatic copolyester,poly(tetramethylene glutarate-co-terephthalate) containing 30 molepercent terephthalic acid residues, may be prepared by heating dimethylglutarate, dimethyl terephthalate, and 1,4-butanediol first at 200° C.for 1 hour then at 245° C. for 0.9 hour under vacuum in the presence of100 ppm of Ti present initially as titanium tetraisopropoxide.

To ensure that the reaction of the diol component and dicarboxylic acidcomponent by an ester interchange reaction is driven to completion, itis sometimes desirable to employ about 1.05 to about 2.5 moles of diolcomponent to one mole dicarboxylic acid component. Persons of ordinaryskill in the art will understand, however, that the ratio of diolcomponent to dicarboxylic acid component is generally determined by thedesign of the reactor in which the reaction process occurs.

In the preparation of copolyester by direct esterification, i.e., fromthe acid form of the dicarboxylic acid component, polyesters areproduced by reacting the dicarboxylic acid or a mixture of dicarboxylicacids with the diol component or a mixture of diol components and thebranching monomer component. The reaction is conducted at a pressure offrom about 7 kPa gauge (1 psig) to about 1379 kPa gauge (200 psig),preferably less than 689 kPa (100 psig) to produce a low molecularweight copolyester product having an average degree of polymerization offrom about 1.4 to about 10. The temperatures employed during the directesterification reaction typically range from about 180° C. to about 280°C., more preferably ranging from about 220° C. to about 270° C. This lowmolecular weight polymer may then be polymerized by a polycondensationreaction. The polymer presently sold under the name ECOFLEX by BASF hasa glass transition temperature of −33° C. and a melting range of 105 to−115° C.

Polycaprolactone (PCL) is also a biodegradable soft aliphatic polyester,polymer (A), useful in the invention which has a relatively low meltingpoint and a very low glass transition temperature. It is so namedbecause it is formed by polymerizing E-caprolactone. The glasstransition temperature of PCL is −60° C. and the melting point is only60° C. Because of this, PCL and other similar aliphatic polyesters withlow melting points are difficult to process by conventional techniquessuch as film blowing and blow molding. Films made from PCL are tacky asextruded and have low melt strength over 130° C. Also, the slowcrystallization of this polymer causes the properties to change overtime. Blending PCL with other polymers improves the processability ofPCL. One common PCL is TONE, manufactured by Union Carbide. Othermanufactures of PCL include Daicel Chemical, Ltd. and Solvay.

ε-Caprolactone is a seven member ring compound that is characterized byits reactivity. Cleavage usually takes place at the carbonyl group.ε-Caprolactone is typically made from cyclohexanone by a peroxidationprocess. PCL is a polyester made by polymerizing ε-caprolactone. Highermolecular weight PCL may be prepared under the influence of a widevariety of catalysts, such as aluminum alkyls, organometalliccompositions, such as Group Ia, IIa, IIb, or IIIa metal alkyls, Grignardreagents, Group II metal dialkyls, calcium or other metal amides oralkyl amides, reaction products of alkaline earth hexamoniates, alkalineoxides and acetonitrile, aluminum trialkoxides, alkaline earth aluminumor boron hydrides, alkaline metal or alkaline earth hydrides or alkalinemetals alone. PCL is typically prepared by initiation with an aliphaticdiol (HO—R—OH), which forms a terminal end group.

Another “flexible” aliphatic polyester, polymer (A), that may be used inmanufacturing the inventive polymer blends ispolyhydroxybutyrate-hydroxyvalerate copolymer (PHBV), which ismanufactured using a microbial-induced fermentation. One such PHBVcopolyester is manufactured by Monsanto Company and has a glasstransition temperature of about 0° C. and a melting point of about 170°C.

In the fermentation process of manufacturing PHBV, a single bacteriumspecies converts corn and potato feed stocks into a copolymer ofpolyhydroxybutyrate and hydroxyvalerate constituents. By manipulatingthe feed stocks, the proportions of the two polymer segments can bevaried to make different grades of material. All grades are moistureresistant while still being biodegradable. The world producers of PHBVare Monsanto, with its BIOPOL product, and METABOLIX, with its variousgrades of polyhydroxy-alkanoates (PHAs).

Another class of “flexible “aliphatic polyesters, polymers (A), arebased on repeating succinate units such as polybutylene succinate (PBS),polybutylene succinate adipate (PBSA), and polyethylene succinate (PES).Each of these succinate-based aliphatic polyesters are manufactured byShowa High Polymer, Ltd. and are sold under the trade name BIONELLE. PBS(Bionolle 1001) has a glass transition temperature of −30° C. and amelting point of 114° C. PBSA (Bionolle 3001) has a glass transitiontemperature of −35° C. and a melting point of 95° C. PES (Bionolle 6000)has a glass transition temperature of −4° C. and a melting point of 102°C.

The target applications for succinate-based aliphatic polyesters includefilms, sheets, filaments, foam-molded products and foam-expandedproducts. Succinate-based aliphatic polyesters are biodegradable incompost, in moist soil, in water with activated sludge, and in seawater. PBSA degrades rapidly in a compost environment, so it is similarto cellulose, whereas PBS degrades less rapidly and is similar tonewspaper in terms of biodegradation.

Succinic-based aliphatic polyesters are manufactured according to apatented two-step process of preparing succinate aliphatic polyesterswith high molecular weights and useful physical properties. In a firststep, a low molecular weight hydroxy-terminated aliphatic polyesterprepolymer is made from a glycol and an aliphatic dicarboxylic acid.This polymerization is catalyzed by a titanium catalyst such astetraisopropyltitanate, tetraisopropoxy titanium, dibutoxydiacetoacetoxytitanium, or tetrabutyltitanate. In the second step, a high molecularweight polyester is made by reacting a diisocyanate, such ashexamethylene diisocyante (HMDI) with a polyester prepolymer. Somemanufacturers manufacture PBS by first reacting 1,4-butanediol withsuccinic acid in a condensation reaction to form a prepolymer and thenreacting the prepolymer with HMDI as a chain extender.

PBSA copolymer is manufactured by first condensing 1,4-butanediol,succinic acid and adipic acid to form a prepolymer and then reacting theprepolymer with HMDI as a chain extender.

PES homopolymer is prepared by reacting ethylene glycol and succinicacid and using HMDI or diphenylmethane diisocyanate as a chain extender.

In general, those biopolymers (B) that may be characterized as beinggenerally “rigid” or less flexible include those polymers which have aglass transition temperature greater than about 10° C. The stiffbiopolymers (B) will have a glass transition temperature greater thanabout 20° C. In other embodiments of the invention, the rigidbiopolymers (B) will have a glass transition temperature of greater thanabout 30° C., and most preferably greater than above 40° C.

In addition, “rigid” (B) polymers are generally more crystalline thanpolymers (A). The rigid polymers (B) will preferably have aconcentration in a range from about 40% to about 85% by weight of thebiodegradable polymer blend, and in other embodiments, the rigidpolymers (B) will preferably have a concentration in ranges of about 50to about 85% by weight, about 50% to about 75% by weight, and 50% toabout 60% by weight, based on the total weight of the polymer blend.

Examples of rigid biopolymers (B) include but are not limited to thefollowing: polyesteramides (such as those manufactured by Bayer), amodified polyethylene terephthalate (PET) such as those manufactured byDu Pont, biopolymers based on polylactic acid (PLA) (such as thosemanufactured by Cargill-Dow Polymers and Dianippon Ink), terpolymersbased on polylactic acid, polyglycolic acid, polyalkylene carbonates(such as polyethylene carbonate manufactured by PAC Polymers),polyhydroxyalkanoates (PHA), polyhydroxybutyrates (PHB),polyhydroxyvalerates (PHV), polyhydroxybutyrate-hydroxyvaleratecopolymers (PHBV). The biopolymers (B) within the scope of the presentinvention are preferably synthetic polyesters or polyester amides.

In one embodiment, a rigid polymer that may be used in manufacturing thepolymer blends according to the present invention includes polylacticacid (PLA). PLA is a strong thermoplastic material that can be injectionmolded, extruded, thermoformed, or used as spun or melt-blown fibers toproduce nonwoven goods. These polymers of lactic acid(Mn=50,000-110,000) are strong thermoplastics that can be fabricatedinto useful products that can be broken down by common soil bacteriaPotential applications of PLA include paper coatings for packaging (foodand beverage cartons), plastic foam for fast foods, microwavablecontainers, and other consumer products such as disposable diapers oryard waste bags. PLA can be a homopolymer or it may be copolymerizedwith glycolides, lactones or other monomers. One particularly attractivefeature of PLA-based polymers is that they are derived from renewableagricultural products.

Because lactic acid is difficult to polymerize directly to high polymersin a single step on a commercial scale, most companies employ a two-stepprocess. Lactic acid is first oligomerized to a linear chain with amolecular weight of less than 3000 by removing water. The oligomer isthen depolymerized to lactide, which is a cyclic dimer consisting of twocondensed lactic acid molecules. This six-member ring is purified andsubjected to ring opening polymerization to produce polylactic acid witha molecular weight of 50,000-110,000.

Because lactic acid has an a-symmetric carbon atom, it exists in severalisomeric forms. The lactic acid most commonly sold commercially containsequal parts of L-(+)-lactic acid and D-(−)-lactic acid and is thereforeoptically inactive, with no rotatory power. The racemic mixture iscalled DL-lactic acid.

Polylactic acid typically has a glass transition temperature of about59° C. and a melting point of about 178° C. It has low elongation and isquite hard.

Another stiff polymer (B) that may be used within the inventive polymerblends is known as CPLA, which is a derivative of PLA and is sold byDianippon Ink. Two classes of CPLA are sold and are referred to as “CPLArigid” and “CPLA flexible”, both of which are “rigid” polymers as thatterm has been defined herein. CPLA hard has a glass transitiontemperature of 60° C., while CPLA soft has a glass transitiontemperature of 51° C.

Bayer Corporation manufactures polyesteramides sold under the name BAK.One form of BAK is prepared from adipic acid, 1,4-butanediol, and6-aminocaproic acid. BAK 1095, a polyesteramide having an Mn of 22,700and an Mw of 69,700 and which contains aromatic constituents, has amelting point of 125° C. BAK 2195 has a melting point of 175° C.Although the glass transition temperatures of BAK 1095 and BAK 2195 aredifficult to measure, because BAK appears to behave like a stiff polymerin the sense that improved properties may be obtained by blending BAKwith a soft polymer, the inventors believe that the glass transitiontemperature of BAK polymers is essentially at least about

Another stiff polymer (B) that may be used within the inventive polymerblends includes a range of modified polyethylene terephthalate (PET)polyesters manufactured by DuPont, and sold under the trade name BIOMAX.The modified PET polymers of DuPont are described in greater detail inU.S. Pat. No. 5,053,482 to Tietz, U.S. Pat. No. 5,097,004 to Gallagheret al., U.S. Pat. No. 5,097,005 to Tietz, U.S. Pat. No. 5,171,308 toGallagher et al., U.S. Pat. No. 5,219,646, to Gallagher et al., and U.S.Pat. No. 5,295,985 to Romesser et al. For purposes of disclosingsuitable “rigid” polymers that may be used in the manufacture of polymerblends according to the present invention, the foregoing patents aredisclosed herein by specific reference.

In general, the modified PET polymers of DuPont may be characterized ascomprising alternating units of terephthalate and an aliphaticconstituent, with the aliphatic constituent comprising a statisticaldistribution of two or more different aliphatic units derived from twoor more different diols, such as ethylene glycol, diethylene glycol,triethylene oxide, polyethylene glycol, lower alkane diols, bothbranched and unbranched, and derivatives of the foregoing. A portion ofthe aliphatic units may also be derived from an aliphatic diacid, suchas adipic acid. In addition, a small percentage of the phenylene groupswithin the repeating terephthalate units are sulfonated and neutralizedwith an alkali metal or alkaline earth metal base. Both the aliphaticportion of the modified PET polymer as well as the statisticallysignificant quantity of sulfonated terephthalate units contributesignificantly to the biodegradability of the BIOMAX polymer.

Some BIOMAX grades of polymers have a melting point of 200-208° C. and aglass transition temperature of 40-60° C. BIOMAX 6926 is one such grade.It is a relatively strong and stiff polymer and, when blended with asofter polymer, yields excellent sheets and films suitable for wrappingand other packaging materials.

Mitsui Chemicals, Inc. manufactures a terpolymer that includes unitsderived from polylactide, polyglycolide and polycaprolactone that havebeen condensed together. Thus, this polymer is an aliphatic polymer andmay be characterized as a PLA/PGA/PCL terpolymer. Three grades of thispolymer are available, H100J, S100 and T100. The H100J grade PLA/PGA/PCLterpolymer has been analyzed to have a glass transition temperatures of74° C. and a melting point of 173° C.

PAC Polymers Inc. manufactures polyethylene carbonate (PEC) having aglass transition temperature range of 10 to 28° C. PEC is a stiffpolymer for purposes of manufacturing polymer blends according to thepresent invention.

Both polymers (A) and polymers (B) may have an inherent viscosity ofabout 0.2 to about 3.0 deciliters/gram as measured at a temperature of25° C. for a 0.5 g sample in 100 ml of a 60/40 parts by weight solutionof phenol/tetrachloroethane.

The invention may also comprise compatiblizers in the amount of 0.25 to10 weight %. While any compatiblizers known in the art may be used, oneembodiment of the invention includes compatibilizers that arepolyacrylates miscible with polylactic acid. In another embodiment, thecompatibilizers contain methylmethacrylate and/or glycidyl methacrylate.

It is within the scope of the invention to also include a variety ofnatural polymers and their derivatives, such as polymers and derivativesderived from starch, cellulose, other polysaccharides and proteins. Itis also within the scope of the present invention to incorporateinorganic fillers in order to decrease self-adhesion, lower the cost,and increase the modulus of elasticity (Young's modulus) of the polymerblends. In addition, a wide variety of plasticizers may be used in orderto impart desired softening and elongation properties.

The copolyester composition also may comprise a phosphorus-containingflame retardant, although the presence of a flame retardant is notcritical to the invention. The flame retardant may comprise a wide rangeof phosphorus compounds well-known in the art such as, for example,phosphines, phosphites, phosphinites, phosphonites, phosphinates,phosphonates, phosphine oxides, and phosphates.

Examples of phosphorus-containing flame retardants include tributylphosphate, triethyl phosphate, tri-butoxyethyl phosphate, t-butylphenyldiphenyl phosphate, 2-ethylhexyl diphenyl phosphate, ethyl dimethylphosphate, isodecyl diphenyl phosphate, trilauryl phosphate, triphenylphosphate, tricresyl phosphate, trixylenyl phosphate, t-butylphenyldiphenylphosphate, resorcinol bis(diphenyl phosphate), tribenzylphosphate, phenyl ethyl phosphate, trimethyl thionophosphate, phenylethyl thionophosphate, dimethyl methylphosphonate, diethylmethylphosphonate, diethyl pentylphosphonate, dilaurylmethylphosphonate, diphenyl methylphosphonate, dibenzylmethylphosphonate, diphenyl cresylphosphonate, dimethylcresylphosphonate, dimethyl methylthionophosphonate, phenyldiphenylphosphinate, benzyl diphenylphosphinate, methyldiphenylphosphinate, trimethyl phosphine oxide, triphenyl phosphineoxide, tribenzyl phosphine oxide, 4-methyl diphenyl phosphine oxide,triethyl phosphite, tributyl phosphite, trilauryl phosphite, triphenylphosphite, tribenzyl phosphite, phenyl diethyl phosphite, phenyldimethyl phosphite, benzyl dimethyl phosphite, dimethylmethylphosphonite, diethyl pentylphosphonite, diphenylmethylphosphonite, dibenzyl methylphosphonite, dimethylcresylphosphonite, methyl dimethylphosphinite, methyldiethylphosphinite, phenyl diphenylphosphinite, methyldiphenylphosphinite, benzyl diphenylphosphinite, triphenyl phosphine,tribenzyl phosphine, and methyl diphenyl phosphine.

The term “phosphorus acid” as used in describing thephosphorus-containing flame retardants useful in the invention includethe mineral acids such as phosphoric acid, acids having directcarbon-to-phosphorus bonds such as the phosphonic and phosphinic acids,and partially esterified phosphorus acids which contain at least oneremaining unesterified acid group such as the first and second degreeesters of phosphoric acid and the like. Typical phosphorus acids thatcan be employed in the present invention include, but are not limitedto: dibenzyl phosphoric acid, dibutyl phosphoric acid, di(2-ethylhexyl)phosphoric acid, diphenyl phosphoric acid, methyl phenyl phosphoricacid, phenyl benzyl phosphoric acid, hexylphosphonic acid,phenylphosphonic acid tolylphosphonic acid, benzylphosphonic acid,2-phenylethylphosphonic acid, methylhexylphosphinic acid,diphenylphosphinic acid, phenylnaphthylphosphinic acid,dibenzylphosphinic acid, methylphenylphosphinic acid, phenylphosphonousacid, tolylphosphonous acid, benzyl-phosphonous acid, butyl phosphoricacid, 2-ethyl hexyl phosphoric acid, phenyl phosphoric acid, cresylphosphoric acid, benzyl phosphoric acid, phenyl phosphorous acid, cresylphosphorous acid, benzyl phosphorous acid, diphenyl phosphorous acid,phenyl benzyl phosphorous acid, dibenzyl phosphorous acid, methyl phenylphosphorous acid, phenyl phenylphosphonic acid, tolyl methylphosphonicacid, ethyl benzylphosphonic acid, methyl ethylphosphonous acid, methylphenylphosphonous acid, and phenyl phenylphosphonous acid. The flameretardant typically comprises one or more monoesters, diesters, ortriesters of phosphoric acid. In another example, the flame retardantcomprises resorcinol bis(diphenyl phosphate), abbreviated herein as“RDP”.

The flame retardant may be added to the polymer blends at aconcentration of about 5 weight % to about 40 weight % based on thetotal weight of the copolyester composition. Other embodiments of theflame retardant levels are about 7 weight % to about 35 weight %, about10 weight % to about 30 weight %, and about 10 weight % to about 25weight %. The flame retardant copolyester compositions of the presentinvention typically give a V2 or greater rating in a UL94 burn test. Inaddition, our flame retardant copolyester compositions typically give aburn rate of 0 in the Federal Motor Vehicle Safety Standard 302(typically referred to as FMVSS 302).

Oxidative stabilizers also may be included in the polymer blends of thepresent invention to prevent oxidative degradation during processing ofthe molten or semi-molten material on the rolls. Such stabilizersinclude esters such as distearyl thiodipropionate or dilaurylthiodipropionate; phenolic stabilizers such as IRGANOX® 1010 availablefrom Ciba-Geigy AG, ETHANOX® 330 available from Ethyl Corporation, andbutylated hydroxytoluene; and phosphorus containing stabilizers such asIrgafos® available from Ciba-Geigy AG and WESTON® stabilizers availablefrom GE Specialty Chemicals. These stabilizers may be used alone or incombinations.

In addition, the polymer blends may contain dyes, pigments, andprocessing aids such as, for example, fillers, matting agents,antiblocking agents, antistatic agents, blowing agents, chopped fibers,glass, impact modifiers, carbon black, talc, TiO2 and the like asdesired. Colorants, sometimes referred to as toners, may be added toimpart a desired neutral hue and/or brightness to the copolyester andthe end use product. Preferably, the copolyester compositions also maycomprise 0 to about 30 weight % of one or more processing aids to alterthe surface properties of the composition and/or to enhance flow.Representative examples of processing aids include calcium carbonate,talc, clay, TiO2, NH4Cl, silica, calcium oxide, sodium sulfate, andcalcium phosphate. Further examples of processing aid amounts within thecopolyester composition of the instant invention are about 5 to about 25weight % and about 10 to about 20 weight %. Preferably, the processingaid is also a biodegradation accelerant, that is, the processing aidincreases or accelerates the rate of biodegradation in the environment.In the context of the invention, it has been discovered that processingaids that also may function to alter the pH of the compostingenvironment such as, for example, calcium carbonate, calcium hydroxide,calcium oxide, barium oxide, barium hydroxide, sodium silicate, calciumphosphate, magnesium oxide, and the like may also accelerate thebiodegradation process. For the present invention, the preferredprocessing aid is calcium carbonate.

It is preferred that the polymer blends of the invention have anunnotched Izod impact strength according to ASTM D256 of at least 9ft-lbs/in at 0° C. and at 23° C., and in another embodiment, at least 20ft-lbs/in at 23° C.

The polymers (A) and (B) of the invention are biodegradable and also maycontain biodegradable additives to enhance their disintegration andbiodegradability in the environment. The copolyester compositions maycomprise about 1 to about 50 weight % of a biodegradable additive. Otherexamples of biodegradable additive levels are about 5 to about 25 weight% and about 10 to about 20 weight %. One effect of such additives is toincrease the biodegradability of the copolyester composition and tocompensate for reduced biodegradability resulting from highconcentrations of various additives.

Representative examples of the biodegradable additives which may beincluded in the copolyester compositions of this invention includemicrocrystalline cellulose, polylactic acid, polyhydroxybutyrate,polyhydroxyvalerate, polyvinyl alcohol, thermoplastic starch or othercarbohydrates, or combination thereof. Preferably, the biodegradableadditive is a thermoplastic starch. A thermoplastic starch is a starchthat has been gelatinized by extrusion cooking to impart a disorganizedcrystalline structure. As used herein, thermoplastic starch is intendedto include “destructured starch” as well as “gelatinized starch”, asdescribed, for example, in Bastioli, C. Degradable Polymers, 1995,Chapman & Hall: London, pages 112-137. By gelatinized, it is meant thatthe starch granules are sufficiently swollen and disrupted that theyform a smooth viscous dispersion in the water. Gelatinization iseffected by any known procedure such as heating in the presence of wateror an aqueous solution at temperatures of about 60° C. The presence ofstrong alkali is known to facilitate this process. The thermoplasticstarch may be prepared from any unmodified starch from cereal grains orroot crops such as corn, wheat, rice, potato, and tapioca, from theamylose and amylopectin components of starch, from modified starchproducts such as partially depolymerized starches and derivatizedstarches, and also from starch graft copolymers. Thermoplastic starchesare commercially available from National Starch Company.

The various components of the copolyester compositions such as, forexample, the flame retardant, release additive, other processing aids,and toners, may be blended in batch, semicontinuous, or continuousprocesses. Small scale batches may be readily prepared in anyhigh-intensity mixing devices well-known to those skilled in the art,such as Banbury mixers, prior to calendering or other thermalprocessing. The components also may be blended in solution in anappropriate solvent. The melt blending method includes blending thecopolyester, additive, and any additional non-polymerized components ata temperature sufficient to at least partially melt the copolyester. Theblend may be cooled and pelletized for further use or the melt blend canbe processed directly from this molten blend into film or sheet ormolded article, for example. The term “melt” as used herein includes,but is not limited to, merely softening the AAPE. For melt mixingmethods generally known in the polymer art, see “Mixing and Compoundingof Polymers” (I. Manas-Zloczower & Z. Tadmor editors, Carl Hanser VerlagPublisher, 1994, New York, N.Y.). When colored product (e.g. sheet,molded article, or film is desired, pigments or colorants may beincluded in the copolyester coposition during the reaction of the dioland the dicarboxylic acid or they may be melt blended with the preformedcopolyester. A preferred method of including colorants is to use acolorant having thermally stable organic colored compounds havingreactive groups such that the colorant is copolymerized and incorporatedinto the copolyester to improve its hue. For example, colorants such asdyes possessing reactive hydroxyl and/or carboxyl groups, including, butnot limited to, blue and red substituted anthraquinones, may becopolymerized into the polymer chain. When dyes are employed ascolorants, they may be added to the copolyester reaction process afteran ester interchange or direct esterification reaction.

The polymer compositions of the invention comprise a plasticizercombined with a polymer as described herein. The presence of theplasticizer is useful to enhance flexibility and the good mechanicalproperties of the resultant film or sheet or molded object. Theplasticizer also helps to lower the processing temperature of thepolyesters. The plasticizers typically comprise one or more aromaticrings. The preferred plasticizers are soluble in the polyester asindicated by dissolving a 5-mil (0.127 mm) thick film of the polyesterto produce a clear solution at a temperature of 160° C. or less. Morepreferably, the plasticizers are soluble in the polyester as indicatedby dissolving a 5-mil (0.127 mm) thick film of the polyester to producea clear solution at a temperature of 150° C. or less. The solubility ofthe plasticizer in the polyester may be determined as follows:

-   1. Placing into a small vial a ½ inch section of a standard    reference film, 5 mils (0.127 mm) in thickness and about equal to    the width of the vial.-   2. Adding the plasticizer to the vial until the film is covered    completely.-   3. Placing the vial with the film and plasticizer on a shelf to    observe after one hour and again at 4 hours. Note the appearance of    the film and liquid.-   4. After the ambient observation, placing the vial in a heating    block and allow the temperature to remain constant at 75° C. for one    hour and observe the appearance of the film and liquid.-   5. Repeating step 4 for each of the following temperatures (° C.):    100, 140, 150, and 160.

Examples of plasticizers potentially useful in the invention are asfollows:

TABLE A Plasticizers Adipic Acid Derivatives Dicapryl adipateDi-(2-ethylhexyl adipate) Di(n-heptyl,n-nonyl) adipate Diisobutyladipate Diisodecyl adipate Dinonyl adipate Di-(tridecyl) adipate AzelaicAcid Derivatives Di-(2-ethylhexyl azelate) Diisodecyl azelate Diisoctylazealate Dimethyl azelate Di-n-hexyl azelate Benzoic Acid DerivativesDiethylene glycol dibenzoate (DEGDB) Dipropylene glycol dibenzoatePropylene glycol dibenzoate Polyethylene glycol 200 dibenzoate Neopentylglycol dibenzoate Citric Acid Derivatives Acetyl tri-n-butyl citrateAcetyl triethyl citrate Tri-n-Butyl citrate Triethyl citrate Dimer AcidDerivatives Bis-(2-hydroxyethyl dimerate) Epoxy Derivatives Epoxidizedlinseed oil Epoxidized soy bean oil 2-Ethylhexyl epoxytallate FumaricAcid Derivatives Dibutyl fumarate Glycerol Derivatives GlycerolTribenzoate Glycerol triacetate Glycerol diacetate monolaurateIsobutyrate Derivative 2,2,4-Trimethyl-1,3-pentanediol, DiisobutyrateTexanol diisobutyrate Isophthalic Acid Derivatives Dimethyl isophthalateDiphenyl isophthalate Di-n-butylphthalate Lauric Acid Derivatives Methyllaurate Linoleic Acid Derivative Methyl linoleate, 75% Maleic AcidDerivatives Di-(2-ethylhexyl) maleate Di-n-butyl maleate MellitatesTricapryl trimellitate Triisodecyl trimellitate Tri-(n-octyl,n-decyl)trimellitate Triisonyl trimellitate Myristic Acid Derivatives Isopropylmyristate Oleic Acid Derivatives Butyl oleate Glycerol monooleateGlycerol trioleate Methyl oleate n-Propyl oleate Tetrahydrofurfuryloleate Palmitic Acid Derivatives Isopropyl palmitate Methyl palmitateParaffin Derivatives Chloroparaffin, 41% C1 Chloroparaffin, 50% C1Chloroparaffin, 60% C1 Chloroparaffin, 70% C1 Phosphoric AcidDerivatives 2-Ethylhexyl diphenyl phosphate Isodecyl diphenyl phosphatet-Butylphenyl diphenyl phosphate Resorcinol bis(diphenyl phosphate)(RDP) 100% RDP Blend of 75% RDP, 25% DEGDB (by wt) Blend of 50% RDP, 50%DEGDB (by wt) Blend of 25% RDP, 75% DEGDB (by wt) Tri-butoxyethylphosphate Tributyl phosphate Tricresyl phosphate Triphenyl phosphatePhthalic Acid Derivatives Butyl benzyl phthalate Texanol benzylphthalate Butyl octyl phthalate Dicapryl phthalate Dicyclohexylphthalate Di-(2-ethylhexyl) phthalate Diethyl phthalate Dihexylphthalate Diisobutyl phthalate Diisodecyl phthalate Diisoheptylphthalate Diisononyl phthalate Diisooctyl phthalate Dimethyl phthalateDitridecyl phthalate Diundecyl phthalate Ricinoleic Acid DerivativesButyl ricinoleate Glycerol tri(acetyl) ricinlloeate Methyl acetylricinlloeate Methyl ricinlloeate n-Butyl acetyl ricinlloeate Propyleneglycol ricinlloeate Sebacic Acid Derivatives Dibutyl sebacateDi-(2-ethylhexyl) sebacate Dimethyl sebacate Stearic Acid DerivativesEthylene glycol monostearate Glycerol monostearate Isopropyl isostearateMethyl stearate n-Butyl stearate Propylene glycol monostearate SuccinicAcid Derivatives Diethyl succinate Sulfonic Acid Derivatives N-Ethylo,p-toluenesulfonamide o,p-toluenesulfonamide

Solubility of the plasticizers also can be predicted using solubilityparameter determinations as described by Michael M. Coleman, John E.Graf, and Paul C. Painter, in their book, Specific Interactions and theMiscibility of Polymer Blends, solubility values were ascribed tovarious plasticizers in the test. A solubility value can be ascribed toEASTAR™ BIO of 10.17 (cal/cc)½. Evaluation of the experimental data byColeman and others, with a comparison to solubility values of eachplasticizer suggests that if a solvent/plasticizer falls within 2(cal/cc)½ plus or minus of the value ascribed for the polymer, that thesolvent/plasticizer will be compatible at some level with the polymer.Furthermore, the closer a plasticizer solubility values is to that ofthe AAPE copolyester, the more compatible it would be. However,solubility parameters are not absolute as that many forces are acting inconjunction when two molecules meet, especially as that theplasticizer/solvent is extremely small in comparison to themacromolecule of a polymer and simply that there are some that are notpurely the named material. For instance, in the case of dipropyleneglycol dibenzoate, the commercially prepared material may include levelsof dipropylene glycol monobenzoate, propylene glycol dibenzoate and itsmonobenzoate as well as the potential for multiple polypropylene glycolgroups.

A similar test to that above is described in The Technology ofPlasticizers, by J. Kern Sears and Joseph R. Darby, published by Societyof Plastic Engineers/Wiley and Sons, New York, 1982, pp 136-137. In thistest, a grain of the polymer is placed in a drop of plasticizer on aheated microscope stage. If the polymer disappears, then it issolubilized. The plasticizers can also be classified according to theirsolubility parameter. The solubility parameter, or square root of thecohesive energy density, of a plasticizer can be calculated by themethod described by Coleman et al., Polymer 31, 1187 (1990). The mostpreferred plasticizers will have a solubility parameter (δ) in the rangeof about 8.17 to about 12.17 (cal/cc)½. It is generally understood thatthe solubility parameter of the plasticizer should be within 2.0 unitsof the solubility parameter of the polyester, preferably less than 1.5unit of the solubility parameter of the polyester, and more preferably,less than 1.0 unit of the solubility parameter of the polyester.

Examples of plasticizers which may be used according to the inventionare esters comprising: (i) acid residues comprising one or more residuesof: phthalic acid, adipic acid, trimellitic acid, benzoic acid, azelaicacid, terephthalic acid, isophthalic acid, butyric acid, glutaric acid,citric acid or phosphoric acid; and (ii) alcohol residues comprising oneor more residues of an aliphatic, cycloaliphatic, or aromatic alcoholcontaining up to about 20 carbon atoms. Further, non-limiting examplesof alcohol residues of the plasticizer include methanol, ethanol,propanol, isopropanol, butanol, isobutanol, stearyl alcohol, laurylalcohol, phenol, benzyl alcohol, hydroquinone, catechol, resorcinol,ethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, anddiethylene glycol. The plasticizer also may comprise one or morebenzoates, phthalates, phosphates, or isophthalates.

In one embodiment, the preferred plasticizers are selected from thegroup consisting of N-ethyl-o,p-toluenesulfonamide, 2-ethylhexyldiphenyl phosphate, isodecyl diphenyl phosphate, tributyl phosphate,t-butylphenyl diphenyl phosphate, tricresyl phosphate, chloroparaffin(60% chlorine), chloroparaffin (50% chlorine), diethyl succinate,di-n-butyl maleate, di-(2-ethylhexyl) maleate, n-butyl stearate, acetyltriethyl citrate, triethyl citrate, tri-n-butyl citrate, acetyltri-n-butyl citrate, methyl oleate, dibutyl fumarate, diisobutyladipate, dimethyl azelate, epoxidized linseed oil, glycerol monooleate,methyl acetyl ricinloeate, n-butyl acetyl ricinloeate, propylene glycolricinloeate, polyethylene glycol 200 dibenzoate, diethylene glycoldibenzoate, dipropylene glycol dibenzoate, dimethyl phthalate, diethylphthalate, di-n-butylphthalate, diisobutyl phthalate, butyl benzylphthalate, or glycerol triacetate.

In a second embodiment, the preferred plasticizers are selected from thegroup consisting of N-ethyl-o,p-toluenesulfonamide, 2-ethylhexyldiphenyl phosphate, isodecyl diphenyl phosphate, tributyl phosphate,t-butylphenyl diphenyl phosphate, tricresyl phosphate, chloroparaffin(60% chlorine), chloroparaffin (50% chlorine), diethyl succinate,di-n-butyl maleate, di-(2-ethylhexyl) maleate, n-butyl stearate, acetyltriethyl citrate, triethyl citrate, tri-n-butyl citrate, dimethylazelate, polyethylene glycol 200 dibenzoate, diethylene glycoldibenzoate, dipropylene glycol dibenzoate, dimethyl phthalate, diethylphthalate, di-n-butylphthalate, diisobutyl phthalate, butyl benzylphthalate, or glycerol triacetate.

In a third embodiment, the preferred plasticizers are selected from thegroup consisting of N-ethyl-o,p-toluenesulfonamide, 2-ethylhexyldiphenyl phosphate, isodecyl diphenyl phosphate, t-butylphenyl diphenylphosphate, tricresyl phosphate, chloroparaffin (60% chlorine),chloroparaffin (50% chlorine), diethyl succinate, di-n-butyl maleate,n-butyl stearate, polyethylene glycol 200 dibenzoate, diethylene glycoldibenzoate, dipropylene glycol dibenzoate, dimethyl phthalate, diethylphthalate, di-n-butylphthalate, diisobutyl phthalate, or butyl benzylphthalate.

In a fourth embodiment, the preferred plasticizers are selected from thegroup consisting of N-ethyl-o,p-toluenesulfonamide, 2-ethylhexyldiphenyl phosphate, isodecyl diphenyl phosphate, t-butylphenyl diphenylphosphate, tricresyl phosphate, chloroparaffin (60% chlorine),polyethylene glycol 200 dibenzoate, diethylene glycol dibenzoate,dipropylene glycol dibenzoate, dimethyl phthalate, diethyl phthalate,di-n-butylphthalate, or butyl benzyl phthalate.

In a fifth embodiment, the preferred plasticizers are selected from thegroup consisting of N-ethyl-o,p-toluenesulfonamide, t-butylphenyldiphenyl phosphate, tricresyl phosphate, diethylene glycol dibenzoate,dipropylene glycol dibenzoate, dimethyl phthalate, diethyl phthalate, orbutyl benzyl phthalate.

In a sixth embodiment, the preferred plasticizers are selected from thegroup consisting of N-ethyl-o,p-toluenesulfonamide, diethylene glycoldibenzoate, dipropylene glycol dibenzoate, or dimethyl phthalate.

In a seventh embodiment, diethylene glycol dibenzoate is the preferredplasticizer.

By the term “biodegradable”, as used herein in reference to the AAPE's,polymers (A) and (B), polymer blends, film and sheet, flame retardants,and additives of the present invention, means that polyestercompositions, film, and sheet of this invention are degraded underenvironmental influences in an appropriate and demonstrable time span asdefined, for example, by ASTM Standard Method, D6340-98, entitled“Standard Test Methods for Determining Aerobic Biodegradation ofRadiolabeled Plastic Materials in an Aqueous or Compost Environment”.The AAPE's, polymers (A) and (B), film and sheet, flame retardants, andadditives of the present invention also may be “biodisintegradable”,meaning that these materials are easily fragmented in a compostingenvironment as determined by DIN Method 54900. The AAPE, composition,film and sheet, are initially reduced in molecular weight in theenvironment by the action of heat, water, air, microbes and otherfactors. This reduction in molecular weight results in a loss ofphysical properties (film strength) and often in film breakage. Once themolecular weight of the AAPE is sufficiently low, the monomers andoligomers are then assimilated by the microbes. In an aerobicenvironment, these monomers or oligomers are ultimately oxidized to CO2,H2O, and new cell biomass. In an anaerobic environment, the monomers oroligomers are ultimately oxidized to CO2, H2, acetate, methane, and cellbiomass. Successful biodegradation requires that direct physical contactmust be established between the biodegradable material and the activemicrobial population or the enzymes produced by the active microbialpopulation. An active microbial population useful for degrading thefilms, copolyesters, and copolyester compositions of the invention cangenerally be obtained from any municipal or industrial wastewatertreatment facility or composting facility. Moreover, successfulbiodegradation requires that certain minimal physical and chemicalrequirements be met such as suitable pH, temperature, oxygenconcentration, proper nutrients, and moisture level.

Composting can be defined as the microbial degradation and conversion ofsolid organic waste into soil. One of the key characteristics of compostpiles is that they are self heating; heat is a natural by-product of themetabolic break down of organic matter. Depending upon the size of thepile, or its ability to insulate, the heat can be trapped and cause theinternal temperature to rise. Efficient degradation within compost pilesrelies upon a natural progression or succession of microbial populationsto occur. Initially the microbial population of the compost is dominatedby mesophilic species (optimal growth temperatures between 20 and 45°C.).

The process begins with the proliferation of the indigenous mesophilicmicroflora and metabolism of the organic matter. This results in theproduction of large amounts of metabolic heat which raise the internalpile temperatures to approximately 55-65° C. The higher temperature actsas a selective pressure which favors the growth of thermophilic specieson one hand (optimal growth range between 45-60° C.), while inhibitingthe mesophiles on the other.

Although the temperature profiles are often cyclic in nature,alternating between mesophilic and thermophilic populations, municipalcompost facilities attempt to control their operational temperaturesbetween 55-60° C. in order to obtain optimal degradation rates.Municipal compost units are also typically aerobic processes, whichsupply sufficient oxygen for the metabolic needs of the microorganismspermitting accelerated biodegradation rates.

There are a number of optional components which may be included withinthe biodegradable polymer blends of the present invention in order toimpart desired properties. These include, but are not limited to,plasticizers, flame retardants, illers, natural polymers andnonbiodegradable polymers.

Fillers may optionally be added for a number of reasons, including butnot limited to, increasing the Young's modulus, and decreasing the costand tendency of the polymer blend to “block” or self-adhere duringprocessing. The fillers within the scope of the invention will generallyfall within three classes or categories: (1) inorganic particulatefillers, (2) fibers and (3) organic fillers.

The terms “particle” or “particulate filler” should be interpretedbroadly to include filler particles having any of a variety of differentshapes and aspect ratios. In general, “particles” are those solidshaving an aspect ratio (i.e., the ratio of length to thickness) of lessthan about 10:1. Solids having an aspect ratio greater than about 10:1may be better understood as “fibers”, as that term will be defined anddiscussed hereinbelow.

Virtually any known filler, whether inert or reactive, can beincorporated into the biodegradable polymer blends. In general, addingan inorganic filler will tend to greatly reduce the cost of theresulting polymer blend. If a relatively small amount of inorganicfiller is used, the effects on the strength of the final composition areminimized, while adding a relatively large amount of inorganic fillerwill tend to maximize those effects. In those cases where adding theinorganic filler will tend to detract from a critical physicalparameter, such as tensile strength or flexibility, only so much of thefiller should be added in order to reduce the cost of the resultingcomposition while retaining adequate mechanical properties required bythe intended use. However, in those cases where adding the inorganicfiller will improve one or more desired physical properties of a givenapplication, such as stiffness, compressive strength, it may bedesirable to maximize the quantity of added filler in order to providethis desired property while also proving greatly decreased cost.

Examples of useful inorganic fillers that may be included within thebiodegradable polymer blends include such disparate materials as sand,gravel, crushed rock, bauxite, granite, limestone, sandstone, glassbeads, aerogels, xerogels, mica, clay, alumina, silica, kaolin,microspheres, hollow glass spheres, porous ceramic spheres, gypsumdihydrate, insoluble salts, calcium carbonate, magnesium carbonate,calcium hydroxide, calcium aluminate, magnesium carbonate, titaniumdioxide, talc, ceramic materials, pozzolanic materials, salts, zirconiumcompounds, xonotlite (a crystalline calcium silicate gel), lightweightexpanded clays, perlite, vermiculite, hydrated or unhydrated hydrauliccement particles, pumice, zeolites, exfoliated rock, ores, minerals, andother geologic materials. A wide variety of other inorganic fillers maybe added to the polymer blends, including materials such as metals andmetal alloys (e.g., stainless steel, iron, and copper), balls or hollowspherical materials (such as glass, polymers, and metals), filings,pellets, flakes and powders (such as microsilica).

The particle size or range of particle sizes of the inorganic fillerswill depend on the wall thickness of the film, sheet, or other articlethat is to be manufactured from the polymer blend. In general, thelarger the wall thickness, the larger will be the acceptable particlesize. In most cases, it will be preferable to maximize the particle sizewithin the acceptable range of particle sizes for a given application inorder to reduce the cost and specific surface area of the inorganicfiller. For films that are intended to have a substantial amount offlexibility, tensile strength and bending endurance (e.g., plastic bags)the particle size of the inorganic filler will preferably be less thanabout 10% of the wall thickness of the film. For example, for a blownfilm having a thickness of 40 microns, it will be preferable for theinorganic filler particles to have a particle size of about 4 microns orless.

The amount of particulate filler added to a polymer blend will depend ona variety of factors, including the quantity and identities of the otheradded components, as well as the specific surface area and/or packingdensity of the filler particles themselves. Accordingly, theconcentration of particulate filler within the polymer blends of thepresent invention may be included in a broad range from as low as about5% by volume to as high as about 90% by volume of the polymer blend.Because of the variations in density of the various inorganic fillersthan can be used, it may be more correct in some instances to expressthe concentration of the inorganic filler in terms of weight percentrather than volume percent. In view of this, the inorganic fillercomponents can be included within a broad range from as low as 5% byweight to as high as 95% by weight of the polymer blend.

In those cases where it is desired for the properties of thethermoplastic phase to predominate due to the required performancecriteria of the articles being manufactured, the inorganic filler willpreferably be included in an amount in a range from about 5% to about50% by volume of polymer blend. On the other hand, where it is desiredto create highly inorganically filled systems, the inorganic filler willpreferably be included in an amount in a range from about 50% to about90% by volume.

In light of these competing objectives, the actual preferred quantity ofinorganic filler may vary widely. In general terms, however, in order toappreciably decrease the cost of the resulting polymer blend, theinorganic filler component will preferably be included in an amountgreater than about 15% by weight of the polymer blend, more preferablyin an amount greater than about 25% by weight, more especiallypreferably in an amount greater than about 35% by weight, and mostpreferably in an amount greater than about 50% by weight of the polymerblend. However, the inorganic filler may be included in any amount, suchas in an amount greater than about 3% by weight, preferably greater thanabout 5% by weight, and more preferably greater than about 10% of thepolymer blend.

A wide range of fibers can optionally be used in order to improve thephysical properties of the polymer blends. Like the aforementionedfillers, fibers will typically constitute a solid phase that is separateand distinct from the thermoplastic phase. However, because of the shapeof fibers, i.e., by having an aspect ratio greater than at least about10:1, they are better able to impart strength and toughness thanparticulate fillers. As used in the specification and the appendedclaims, the terms “fibers” and “fibrous material” include both inorganicfibers and organic fibers. Fibers may be added to the moldable mixtureto increase the flexibility, ductility, bendability, cohesion,elongation ability, deflection ability, toughness, dead-fold, andfracture energy, as well as the flexural and tensile strengths of theresulting sheets and articles.

Fibers that may be incorporated into the polymer blends includenaturally occurring organic fibers, such as cellulosic fibers extractedfrom wood, plant leaves, and plant stems. In addition, inorganic fibersmade from glass, graphite, silica, ceramic, rock wool, or metalmaterials may also be used. Preferred fibers include cotton, wood fibers(both hardwood or softwood fibers, examples of which include southernhardwood and southern pine), flax, abaca, sisal, ramie, hemp, andbagasse because they readily decompose under normal conditions. Evenrecycled paper fibers can be used in many cases and are extremelyinexpensive and plentiful. The fibers may include one or more filaments,fabrics, mesh or mats, and which may be co-extruded, or otherwiseblended with or impregnated into, the polymer blends of the presentinvention.

The fibers used in making the articles of the present inventionpreferably have a high length to width ratio (or “aspect ratio”) becauselonger, narrower fibers can impart more strength to the polymer blendwhile adding significantly less bulk and mass to the matrix than thickerfibers. The fibers will have an aspect ratio of at least about 10:1,preferably greater than about 25:1, more preferably greater than about100:1, and most preferably greater than about 250:1.

The amount of fibers added to the polymer blends will vary dependingupon the desired properties of the final molded article, with tensilestrength, toughness, flexibility, and cost being the principle criteriafor determining the amount of fiber to be added in any mix design.Accordingly, the concentration of fibers within the polymer blends ofthe present invention can be included in a broad range from 0% to about90% by weight of the polymer blend. Preferably, fibers will be includedin an amount in a range from about 3% to about 80% by weight of thepolymer blend, more preferably in a range from about 5% to about 60% byweight, and most preferably in a range from about 10% to about 30% byweight of the polymer blend.

The polymer blends of the present invention may also include a widerange of organic fillers. Depending on the melting points of the polymerblend and organic filler being added, the organic filler may remain as adiscrete particle and constitute a solid phase separate from thethermoplastic phase, or it may partially or wholly melt and becomepartially or wholly associated with the thermoplastic phase.

Organic fillers may comprise a wide variety of natural occurring organicfillers such as, for example, seagel, cork, seeds, gelatins, wood flour,saw dust, milled polymeric materials, agar-based materials, and thelike. Organic fillers may also include one or more synthetic polymers ofwhich there is virtually endless variety. Because of the diverse natureof organic fillers, there will not generally be a preferredconcentration range for the optional organic filler component.

Natural polymers may be used within the polymer blends of the presentinvention including derivatives of starch and cellulose, proteins andderivatives thereof, and other polysaccharides such as polysaccharidegums and derivatives thereof, some of which are described in thisapplication as biodegradable additives.

Examples of starch derivatives include, but are not limited to, modifiedstarches, cationic and anionic starches, and starch esters such asstarch acetate, starch hydroxyethyl ether, alkyl starches, dextrins,amine starches, phosphates starches, and dialdehyde starches.

Examples of derivatives of cellulose include, but are not limited to,cellulosic esters (e.g., cellulose formate, cellulose acetate, cellulosediacetate, cellulose propionate, cellulose butyrate, cellulose valerate,mixed esters, and mixtures thereof) and cellulosic ethers (e.g.,methylhydroxyethylcellulose, hydroxymethylethylcellulose,carboxymethylcellulose, methylcellulose, ethylcellulose,hydroxyethylcellulose, hydroxyethylpropylcellulose, and mixturesthereof).

Other polysaccharide-based polymers that can be incorporated into thepolymer blends of the invention include alginic acid, alginates,phycocolloids, agar, gum arabic, guar gum, acacia gum, carrageenan gum,flircellaran gum, ghatti gum, psyllium gum, quince gum, tamarind gum,locust bean gum, gum karaya, xanthan gum, and gum tragacanth, andmixtures or derivatives thereof.

Suitable protein-based polymers include, for example, Zein.RTM. (aprolamine derived from corn), collagen (extracted from animal connectivetissue and bones) and derivatives thereof such as gelatin and glue,casein (the principle protein in cow milk), sunflower protein, eggprotein, soybean protein, vegetable gelatins, gluten and mixtures orderivatives thereof.

Although an important feature of the polymer blends is that they aregenerally considered to be biodegradable, it is certainly within thescope of the invention to include one or more polymers which are notbiodegradable. If the nonbiodegradable polymer generally comprises adisperse phase rather than the dominant continuous phase, polymer blendsincluding a nonbiodegradable polymer will nevertheless be biodegradable,at least in part. When degraded, the polymer blend may leave behind anonbiodegradable residue that nevertheless is superior to entire sheetsand films of nonbiodegradable polymer.

Examples of common nonbiodegradable polymers suitable for forming sheetsand films include, but are not limited to, polyethylene, polypropylene,polybutylene, polyethylene terephthalate (PET), modified PET with1,4-cyclohexanedimethanol (PETG), polyvinyl chloride, polyvinylidenechloride(PVDC) polystyrene, polyamides, nylon, polycarbonates,polysulfides, polysulfones, copolymers including one or more of theforegoing, and the like.

This invention also includes a process for extrusion blow molding anarticle or film or sheet or for making an extrusion profile, or forextruding film or sheet, comprising the polymer blends describedhereinabove, and the films or sheets or extrusion profile or extrusionblow molded article produced therefrom.

The blends of this invention are also useful as molded plastic parts, oras films and/or sheet. Examples of such parts include eyeglass frames,toothbrush handles, toys, automotive trim, tool handles, camera parts,razor parts, ink pen barrels, disposable syringes, bottles, nonwovens,food wraps, packaging films, and the like.

For this invention, including the Examples, the following measurementsapply: The Izod impact strength is measured by ASTM method D256.Inherent viscosities (IV) are measured in dL/g at a temperature of 25°C. for a 0.5 gram sample in 100 ml of a 60/40 by weight solution ofphenol/tetrachloroethane (PM95). Zero shear viscosity is measured bytorque rheometry and is reported in Poise. Glass transition (Tg) andmelting Tm temperatures are measured by DSC at a scan rate of 20°C./min. Abbreviations used herein are as follows: “IV” is inherentviscosity; “g” is gram; “psi” is pounds per square inch; “cc” is cubiccentimeter; “m” is meter; “rpm” is revolutions per minute; “AAPE” isaliphatic aromatic copolyester and, as used in the Examples, refers topoly(tetramethyiene adipate-co-terephthalate) where the mole percent ofadipate to terephthalate is 55/45. PLA is polylactic acid. HeatDeflection Temperature (HDT), at 455 kilopascals (about 66 psi), wasdetermined according to ASTM D648 and is measured in psi. Notched andUnnotched Izod Impact Strength was determined at 23° C. according toASTM D256. Flexural Modulus (Flex Modulus), Yield Strain and YieldStress was determined according to ASTM D790. Tensile properties weredetermined according to ASTM D638. Notched and Unnotched Izod values aregiven in foot pounds per inch (53 Joules per meter=1 foot pound perinch).

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention. Moreover, all patents, patent applications (published orunpublished, foreign or domestic), literature references or otherpublications noted above are incorporated herein by reference for anydisclosure pertinent to the practice of this invention.

EXAMPLES

The polymer blends provided by the present invention and the preparationthereof, including the preparation of representative polyesters, arefurther illustrated by the following examples. The glass transitiontemperatures (Tg's) of the blends were determined using a TA Instruments2950 differential scanning calorimeter (DSC) at a scan rate of 20°C./minute.

In the following Examples, the blends were prepared by the generalmethod: Blends of PLA and AAPE were prepared by compounding on aSterling 1.25 inch single screw extruder. The typical procedure is asfollows: Materials are dried overnight at temperatures between 60 and70° C. to less than 50 ppm moisture content. The components were bagblended and then added at the desired rate using an AccuRate feederthrough a hopper into the barrel of the extruder.

Blends prepared were molded on a Toyo 90 injection molding machine underthe following conditions. These conditions should not be considered theideal conditions, but are typical of those that can be used on blends ofthis type: Nozzle temperature=200° C.; Zone 1 temperature=200° C.; Zone2 temperature=200° C; Zone 3 temperature=200° C.; Zone 4temperature=200° C.; Melt temperature=200° C.; Injection and HoldPressures−900 psig; Mold Temperatures−25° C.; Screw speed−150 rpm.

The melt pressure and extruder amps varied depending on the composition,but ranged between 100 to 150 psi and 4 to 10, respectively.

Afterwards, the strand of material exiting the extruder were quenched inwater and chopped with a pelletizer.

TABLE I Starting materials characterization DSC 1st (° C.) 2nd ZeroShear heat Cool heat Viscosity at 190° C. Material Grade IV in PM95 TgTm Tcc Tg Tm Poise AAPE Eastar Bio 1.061 −31 50, 111 25 −31 113 4323POLYMER AAPE Ecoflex 1.155 −33 104 16 −30 108 21110 PLA PLA 5429B 1.38863 151 58 36460 PLA PLA TE4000 1.105 66 167 62 165 10784 Filler BI008-A−33 77, 112 64 −34 114 concentrate Note the filler concentrate is EastarBio POLYMER compounded as a concentrate with 50 wt % calcium carbonate(Eastar Bio polymer is defined as containing 55 mole % adipic acid, 45mole % terephthalic acid, and 100 mole % 1,4-butanediol, where the totalmole percentages for the diacid components equals 100 mole % and themole percentages for the diol components equals 100 mole %. Ecoflexpolymer sold by BASF contains the same components as Eastar Bio but isalso believed to contain a small amount of branching agent. PLA 5429Band PLA TE-4000 are both polylactic acid but have different viscositiesas shown in Table I. B1008A is 50 weight % Eastar Bio and 50 weight %calcium carbonate.)

TABLE II Blend Characterization Izod 0° C., Notch 0° C., UnNch 23° C.,Notch 23° C., UnNch EnergyAvgAll EnergyAvgAll EnergyAvgAll EnergyAvgAllBI00 Modes Modes Modes Modes Ex. AAPE PLA % 8A % [ft-lb/in] [ft-lb/in][ft-lb/in] [ft-lb/in] 1 65 25 10 10.73 14.06 8.45 11.62 2 15 75 10 0.8811.77 1 15.49 3 75 25 0 9.92 12.51 8.46 8.76 4 50 50 0 2.81 31.75 4.3121.54 5 25 75 0 1.67 9.27 1.93 20.71 6 15 85 0 0.58 5.36 0.58 5.18 7 6525 10 10.13 11.82 7.95 8.97 8 15 75 10 0.74 13.39 0.88 16.54 9 75 25 08.05 13.11 6.16 8.76 10 50 50 0 2.25 21.42 3.12 22.13 11 25 75 0 1.0710.65 1.19 22.7 12 15 85 0 0.58 6.03 0.56 5.12 13 65 25 10 11.74 14.3810.09 11.65 14 15 75 10 0.68 14.69 0.64 17.7 15 75 25 0 11.24 16.93 9.0512.81 16 25 75 0 0.97 9.91 1.08 12.73 17 15 85 0 0.58 5.8 0.57 5.32Examples 1-6 AAPE is Eastar Bio and PLA is Cargill-Dow 5429B Examples7-12 AAPE is Eastar Bio and PLA is Unitika TE4000 Examples 13-17 AAPE isECOFLEX and PLA is Cargill-Dow 5429B(Eastar Bio polymer is a composition comprising terephthalic acid in theamount of 45 mole %, adipic acid in the amount of 55 mole %, and1,4-butanediol in the amount of 100 mole %, wherein the mole percentagesof diol equal a total of 100 mole % and the mole percentages of diacidequal a total of 100 mole %; B 1008A is 50 weight % of Eastar Bio and 50weight % calcium carbonate).

TABLE III Molded Bars - General Mechanical Properties TensileProperties - ASTM D638 Izod Impact Strength - FlexProp 23° C., AverageEnergy 23° C., ASTM D790 Enrgy/ for All Modes [ft-lb/in] Set Yld Yld VolYld HDT 0° C. 23° C. Bio PLA BI008A Temp FlxMdls Strn Strs @Brk StrnYldStrs 264 psi 66 psi 0° C. Un 23° C. Un Blend % % % (° C.) [psi] [%][psi] [lb/in²] [%] [psi] T [° C.] Notched Notched Notched Notched 18 900 10 160 15,636 9 938 22.5 1,077 41 43 6.2 7.0 4.7 6.0 20 90 0 10 20014,542 10 993 26.1 1,119 38 44 6.3 6.4 4.6 5.4 21 65 25 10 160 42,540 81,768 19.0 1,408 40 47 10.1 14.5 7.9 12.0 22 65 25 10 200 43,389 9 1,7873,114 17.2 1,456 41 48 10.7 14.1 8.5 11.6 23 40 50 10 160 164,081 64,781 2,115 7.5 3,104 49 52 2.3 32.5 3.2 31.2 24 40 50 10 200 159,784 64,777 2,077 7.1 3,218 51 54 2.5 30.6 3.6 31.3 25 15 75 10 170 375,847 49,709 715 3.4 7,068 50 52 1.0 11.5 1.1 15.5 26 15 75 10 200 404,006 410,431 723 3.4 7,343 52 53 0.9 11.8 1.0 15.5 27 0 90 10 170 492,017 412,649 372 3.2 8,519 51 52 0.7 8.5 0.8 8.8 28 0 90 10 200 490,769 412,551 660 3.1 8,486 52 54 0.6 8.5 0.8 9.5 29 75 25 0 170 39,575 9 1,77917.9 1,410 40 47 9.8 11.9 7.6 10.4 30 75 25 0 200 43,321 9 1,810 4,26317.9 1,418 42 51 9.9 12.5 8.5 8.8 31 50 50 0 170 145,572 6 4,747 1,9946.3 3,165 49 53 2.7 33.0 3.8 25.7 32 50 50 0 200 149,530 6 4,665 1,0646.3 3,048 51 53 2.8 31.0 4.3 21.5 33 25 75 0 170 335,923 4 8,895 604 3.46,819 50 53 1.6 16.6 1.6 28.2 34 25 75 0 200 329,314 4 8,903 554 3.46,782 52 53 1.7 9.3 1.9 20.7 35 15 85 0 170 419,177 4 11,377 426 3.78,746 50 54 0.6 5.7 0.7 4.7 36 15 85 0 200 428,006 4 11,882 482 3.68,876 52 54 0.6 5.4 0.6 5.2 37 0 100 0 170 517,227 4 14,052 650 3.710,017 51 54 0.5 5.0 0.6 4.2 38 0 100 0 200 510,123 4 13,936 494 3.59,876 53 54 0.6 5.0 0.6 4.1 (Examples 18-\38 - the AAPE is Eastar Bioand the PLA is Cargill-Dow 5429B B1008A is 50 weight % Eastar Bio and 50weight % calcium carbonate)

Based on the above data it is clear that the compositions of interestherein are unique ependent upon the AAPE/PLA blend ratio and not on thenature of the PLA or AAPE itself.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

1. A polymer blend comprising: (A) about 40 to about 50% by weight of alinear, random aliphatic-aromatic copolyester having a glass transitiontemperature of less than about 0° C.; and (B) about 50% by weight of apolylactic acid having a first heat melting point temperature (Tm) of151 to 167° C., said percentages being based on the total weight of thepolymer blend, wherein said polymer blend has an unnotched Izod impactstrength according to ASTM D256 of at least 20 ft-lbs/in at 0° C.
 2. Thepolymer blend according to claim 1, wherein said aliphatic-aromaticcopolyester comprises: (1) diacid residues comprising 40 to 60 molepercent of terephthalic acid residues and 60 to 40 mole percent ofadipic acid residues, glutaric acid residues, or mixtures thereof; and(2) diol residues of 1,4-butanediol.
 3. A film or sheet comprising thepolymer blend according to claim
 1. 4. The film or sheet according toclaim 3, which is produced by extrusion or calendering.
 5. An injectionmolded article comprising the polymer blend according to claim
 1. 6. Anarticle of manufacture according to claim 1, which is formed byextrusion blow molding or profile extrusion.